1. Technical Field
The present invention relates to handover mechanisms for mobile radio devices and, more particularly, to simplifying signaling used to carry out a change in a serving High Speed Downlink Shared Channel (HS-DSCH) cell change.
2. Discussion of Related Art
The Third Generation Partnership Project (3GPP) Release 5 (Rel5) introduced a new HS-DSCH transport channel.
From the 3GPP Release 6 Technical Specification TS 25.308 v6.1.0 (2004-03), it is set forth in Chapter 9 that mobile evaluated handover mechanisms provide the Radio Resource Control (RRC) connection mobility in a CELL_DCH state (see 3GPP TS 25.331 v6.2.0 (2004-06) Chapter 7.1 for an overview of the RRC states and state transitions including GSM). The mobility procedures are affected by the fact that the High Speed Physical downlink shared channel (HS-PDSCH) allocation for a given user equipment (UE) belongs to only one of the radio links assigned to the UE, the serving HS-DSCH radio link. The cell associated with the serving HS-DSCH radio link is defined as the serving HS-DSCH cell.
When conditions for an Active Set Update (ASU) (see 3GPP TS 25.331 v6.2.0 (2004-06) Release 6, Chapter 8.3.4 Active Set Update) and Serving HS-DSCH cell change (see 3GPP TS 25.308 v6.1.0 (2004-03) Release 6, Chapter 9, Mobility Procedures) become simultaneously effective, i.e. when the serving HS-DSCH cell operation is to be moved to the other active set cell and active set of the UE is to be modified (adding new cell (1A), or replacing existing cell with new one (1B), RRC procedures involved (Active Set Update (ASU) and Radio Bearer Control) must be performed separately, one after the other. Depending on scenario either the ASU or Radio Bearer Control procedure is performed first. If the ASU is performed first, the Radio Bearer Control Procedure is delayed introducing performance degeneration to HS-DSCH transmission, which can critical for maintaining the connection, especially when SRBs are mapped on HS-DSCH (required when introducing Fractional DPCH). In other scenario, the Radio Bearer Control procedure containing the necessary HS-DSCH information is needed to be performed first followed by ASU, due to fact that current serving HS-DSCH cell needs to be removed from the UEs AS before RNC is able to add new cell to the AS. This introduces a rather long delay for the ASU, potentially risking the connection. In some cases this delay could not be tolerated and ASU has to be performed first causing a rather long break in HS-DSCH transmission instead.